Tanning with acetonylacetone



United States Patent TANNING WITH ACETONYLACET ONE Edward H. Harris, Jr., and Edward M. Filachione, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed Feb. 20, 1956, Ser. No. 566,735

4 Claims. (Cl. 8-94.33)

(Granted under Title 35, US. Code (1952), see. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to a new reagent and new processes for tanning hides. By the term hides" we mean to include all animal hides and skins that are commonly tanned, including particularly cowhides, horsehides, calfskins, pigskins, sheepskins, goatskins and furskins.

It is an object of this invention to provide new and eflicient tanning agents and tanning processes.

We have discovered that acetonylacetone is -an excellent tanning agentwhen used under certain conditions.

To yield a satisfactory tannage, acetonylacetone must be used alone, in an inert organic solvent, or in aqueous solution of pH in the range of about 7 to 11. At pH below about 5 it exerts no tanning action; in the pH range .5-7 it tans but the resulting leather is very hard and brittle; in 'the' pH range 7-11 rapid tannage is is achieved and the leather produced is soft and flexible,

even without oiling or other softening treatment.

The affinity of acetonylacetone for hide substance is such that even very dilute aqueous solutions in contact with hides are substantially exhausted by absorption of centrated solutions, or even the pure ketone without diluent, are used, any excess of ketone over the amount needed to tan the hide (about 4% by weight) is left in the solution and may be used to tan a subsequent batch of hides. This valuable property permits the use of concentrated solutions of the tanning agent and at the same time avoids loss of the material in partially spent solutions.

Because of the inherent economy and convenience of operating with aqueous solutions rather than with solutions in organic solvents, we prefer to use acetonylacetone in moderately concentrated aqueous solutions such as, for instance, those containing about 5 to 25% of ketone. However, inert organic solvents may be used if desired, suitable ones being the lower aliphatic ketones, alcohols or esters.

No special preparation of the hide to be tanned is required for our process and the tanning may be done at any stage after the liming and unhairing stage of the usual beamhouse operations.

. .40 the ketone into the hides. On the other hand, when con- The pH of the tanning solutions used in our process may be adjusted and maintained in the proper range of 7 to 11 by addition of any suitable bufier system, such as the citrate, acetate, carbonate or similar system in which a strong alkali is combined with a weak acid.

Inorganic salts may be used in the same Way and for the same purposes as in conventional tannages. Thus, such salts as sodium, calcium or magnesium chloride or sulfate may be added to the tanning solution to regulate its osmotic pressure and to aid in the even and uniform penetration and tanning of the hide.

The use of acetonylacetone as a tanning'agent is especially advantageous when applied as one step of a combination tannage wherein the hide is pretanned or retanned with a conventional tanning agent such as chrome or, in particular, vegetable tannins. Thus, when hides tanned with acetonylacetone are retanned with a vegetable tannin, high shrink temperatures are obtained, the shrinkage is reversible and, most important, the leather after being shrunk in hot waterregains both its original dimensions and its soft, flexible, leatherlike properties upon being dried.

The practice of the invention is illustrated by the following examples:

EXAMPLES 1-15 General procedure-The hide substance used was pickled calfskins obtained from local tanneries. These were brought to the isoelectric point (pH about 5) with acetic acid-sodium acetate buffer, washed with Water, and dehydrated by immersion in several changes of acetone. The dehydrated hides were cut into 1 x 3 inch strips which were then stored and wet back with water prior to tanning with acetonylacetone.

A total of approximately 10 grams of the acetone dehydrated calfskin were wet back in water and treated with 50 ml. of a 10% aqueous solution of acetonylacetone in water. The tanning was carried out in rotating bottles in the presence of various buffers and salts. Periodically samples were removed, washed for one day and the shrinkage temperature, Ts, determined on a small specimen by a procedure essentially equivalent to the Official Method of the American Leather Chemists Association. The Ts of the skin before tanning was C. The remainder of the sample was permitted to air dry and was examined for leather characteristics. The results of various tanning treatments on calfskin are summarized in Table I. No tanning was effected at pH of about 3.5 (Examples 1 and 2). Poor leathers which were quite rigid were obtained in the pH range of about 5 to 7 (Examples 3-9). Excellent leathers, which were soft and flexible resulted from tanning in the more alkaline pH range of approximately 7 to 11 (Examples 9-14) after treatment from one to three days. The leather was tan to orange-tan in color, soft and flexible with a fine grain appearance. Even in the unoiled state the leather could be bent double without showing grain crack or pebbly grain. The best leathers were obtained by treatment of calfskin from 1 to 3 days with acetonylacetone as in Examples 10, 11, 13 and 14.

Table I smut-Ne or 'GALFSKIN' WITH ACETONYLAGET'ONE Shrinkage Temp., 0.,

After- Leather Example Treatment, Buffer Salt pH Character 8 hrs. 1 day 3 days 5 days Lactic acid, 0.2 M- 3. 3-2. 7 50 52 53 50 None. Lactic acid, 0.2 M 3. 4 47 50 62 62 Poor. N32 citrate, 0.2 M. 5. 3 61 62 65 68 Stifi. Nag citrate, 0.2 M- 4. 9-4. 7 61 64 68 70 Poor.

5. 6-5. 2 58 62 65 68 Stiff. 5. 6-5. 3 60 63 67 70 Stifi. 6. 5-6. 4 62 64 68 70 Poor. 6. 6-6. 4 62 65 71 73 Stifi. 8. 8-8. 7 63 65 70 74 Good. 9. 7-9. 8 64 69 71 77 Excellent. 9. 9-9. 6 65 72 76 79 Excellent.

'10. 1'9. 9'. 63 68 72 76 Excellent. None 10. 5-8. 4 64 70 74 78 Excellent. NB7SO4- 11. 2-10. 5 63 63 64 63 Poor.v

-,The salt, where used, was sufliclent to result in a aqueous solutidn of salt.

EXAMPLE 16 Approximately 10 grams of acetone dehydrated cow- 9 after washing dried out to an orange-tan colored leather.

EXAMPLE 17 Calfskin was tanned with acetonylacetone as in EX- ample 11. This leather, about 28 grams, was then retanned with canaigre extract, 10 grams of a 90% pure extract (prepared as in U.S. Patent'2,694,725) in 90 grams ofwater, for two days. The pH was maintained at about 3.6 during theretannage by addition of lacticacid. The retanned leather showed a weight gain of about percent. The shrinkage temperature was 88 C. "The canaigre 'retanned leather showed the unusual property of reversible shrinkage, that is the test specimen after having been shrunk by'heating in water recovered its original length upon being placed in cool water. After then being dried the leather had dimensions, appearance and physicalproperties substantially identical to those of .the original sample before shrinkage.

The use of other vegetable tannins in place of the canaigre tannin of the above experiment yields quite similar results.

While we have used only cowhide and calfskin in the above examples and have used acetonylacetone only in aqueous solutions, substantially equivalent results are obtained with other hides and skins and with solvents other than water or with no solvent.

Thus, acetone, methyl ethyl ketone, methanol, isopropanol or, in general, any lower aliphatic ketone, alcohol or ester, may. be used as the solvent for acetonylacetone in the tanning process.

We claim: 7 V

1 A process comprising tanning hides with acetonylacetone as the tanning agent at a pH of about from 7 to 11 for about from 1 to 3 days.

2, A process comprising tanning hides with an aqueous solution containing acetonylacetone as the tanning agent at a pH of about from 7 to 11 for about from 1 to 3 days.

3. A process comprising tanning-hides with acetonylacetone as the tanning agent at a pH of about from 7 to 11 for about from 1 to 3 days and then retanning the V tanned hides with a vegetable tannin.

'4. A process comprising tanning hides with an aqueous solution containing acetonylacetone as the tanning agent at a pH of about from 7 toll for about from 1 to 3 days and then'retanning the tanned hides with an aqueous solution containing a vegetable tannin.

References Cited in the file of this patent UNITED STATES- PATENTS OTHER REFERENCES Gustavson: fThe Chem. and Reactivity of Collagen, Acad. Press, N.Y., 1956, p.233, 292.

Progress in Leather Sci., 1920-45,Br. Leather Mal'luf. Asso. 1948, p. 576, 458, 459. 

4. A PROCESS COMPRISING TANNING HIDES WITH AN AQUEOUS SOLUTION CONTAINING ACETONYLACETONE AS THE TANNING AGENT AT A PH OF ABOUT FROM 7 TO 11 FOR ABOUT FROM 1 TO 3 DAYS AND THEN RETANNING THE TANNED HIDES WITH AN AQUEOUS SOLUTION CONTAINING A VEGETABLE TANNIN. 